ISS will retain its Atlanta offices and will be run as a business unit within IBM's Global Services group. The ISS business unit will be led by Thomas Noonan, formerly the CEO of ISS. No layoffs are planned as a result of the deal.

IBM plans to maintain the ISS Proventia and Managed and Professional Security Services offerings and to eventually integrate them with other products in its portfolio.

The acquisition of ISS, the fifth-largest in IBM's history, means that the company gains a strong position in the $22 billion managed security services market.

This industry is undergoing a round of consolidation as early leaders are being snapped up by larger companies. In June, EMC bought RSA security, in a deal estimated at about $2.1 billion.